The present invention relates to a gasket with a compressible sealing member and a hard support layer for sealing around a hole. The gasket of the invention is used for an internal combustion engine, especially for sealing around a hole where moderate temperature and pressure are applied, such as around an oil hole and an oil pan. However, the gasket may be used, of course, for other general purposes.
In sealing around a hole where moderate temperature and pressure are applied, a gasket member may be formed of an elastic member, or the gasket member may be provided on a base plate with a soft sealing material around a hole to be sealed. However, when the gasket is tightened between engine parts by bolts, portions of the gasket near the bolt holes are especially strongly compressed, so that the portions near the bolt holes lose compressibility or resiliency in a long usage to thereby cause leakage thereat.
In order to obviate the above problems, U.S. Pat. No. 5,975,540 was proposed, wherein a resilient member made of foamed rubber is formed on at least one side of a base metal plate. In this gasket, after the foamed rubber is applied on the base metal plate around a hole to be sealed, parts of the foamed rubber near the bolt holes where the high tightening pressures by the bolts are applied are compressed to reduce resiliency or eliminate foams thereat. Since the resiliency near the bolt holes is eliminated by the compression treatment, tightening pressures applied by the bolts are not lost in a long usage, so that the gasket can be used for a long time without gas leakage. However, it requires a step of eliminating compressibility or resiliency at the parts of the foamed rubber.
The present invention has been made in view of the above, and an object of the invention is to provide a gasket with a compressible sealing member and a hard support layer, wherein decrease of tightening pressure by a bolt due to compression of the sealing member can be prevented or eliminated.
Another object of the invention is to provide a gasket as stated above, which can be manufactured easily at a low cost.
Further objects and advantages of the invention will be apparent from the following description of the invention.
A gasket of the invention is basically formed of a gasket member extending substantially throughout an entire area to be sealed, a compressible sealing member, and a hard coating, both being formed on the gasket member. The gasket member includes a first hole to be sealed, and a plurality of second holes for allowing bolts to pass therethrough. The second holes are arranged around the first hole.
The compressible sealing member is disposed on at least one side of the gasket member to surround the first hole adjacent thereto without surrounding the second holes. The hard coating is disposed on the same side as that of the compressible sealing member to surround the second holes. The hard coating is formed independently from the compressible sealing member, and does not substantially have compressibility.
Since the hard coating is formed around the bolt holes, when the gasket is tightened by the bolts, the hard coating is not substantially compressed or flattened around the bolt holes. Thus, the compressible sealing member surrounding the first hole is not completely compressed, and the resiliency thereof is not reduced so much in a long usage. Thus, the gasket can be used for a long time.
Also, in the invention, the compressible sealing member and the hard coating are formed separately on the gasket member. It is not required to compress a part of the compressible sealing member, as required in U.S. Pat. No. 5,975,540. Thus, the manufacturing process of the gasket is simplified, and it is possible to provide the gasket at a low cost.
In the invention, the hard coating is formed of a material different from that of the compressible sealing member. Preferably, the hard coating is hard rubber or resin, and the compressible sealing member may be a soft rubber or foam rubber.
In the invention, the hard coading is spaced from the compressible sealing member with a gap therebetween. The hard coating may be formed in each of the areas around the second holes to be spaced apart from each other, or the hard coating may be formed continuously to surround the compressible sealing member.